Lactoferrin plays an important role in iron transport and utilization in humans. A glycoprotein containing about 6% sugar and having a total molecular weight of about 80,000 daltons, human lactoferrin is capable of binding two ferric ions with high affinity. Although lactoferrin binds iron tightly, the binding is reversible so that the metal is available upon demand to cells with a need for this essential element. The metal is captured by the side chains of specific amino acids: two tyrosines, one histidine and one aspartate which in combination form a cleft in the surface of the protein. That portion of the protein which contains the aforesaid four amino acids and forms the cleft is termed the "iron-binding domain." Each natural lactofeltin molecule has two iron-binding domains.
Human milk is high in lactoferrin content. The high degree of iron absorption from human milk is manifested in a low incidence of iron deficiency anemia among breast fed infants compared to infants fed with cow's milk. Accordingly, lactoferrin is a key protein for healthy development of infants. Lactoferrin also plays an important role in cell-mediated host immunity. It is present in high concentrations in all bodily secretions, such as tears, sweat, and ciliated respiratory mucous. Because it sequesters iron, lactoferrin can neutralize pathogenic microorganisms by preventing them from obtaining necessary iron at the site of entry, thereby preventing the spread of infection.
Although iron is an essential material in humans, excess iron in the body can induce pathological conditions as well. Chronic iron overload, known as hemosiderosis, is characterized by a greater than normal local or generalized deposition of iron within certain body tissues. Lactoferrin helps to manage the balance of free iron in the body to prevent occurrence of such pathological states in healthy individuals.
The severely limited amount of human milk, the major source of human lactoferrin, restricts lactoferrin production. Furthermore, production of lactoferrin from human milk presents a risk factor of infectious contamination. That is, it could carry with it a potentially lethal contaminant, such as the human immunodeficiency virus (HIV) or another undesirable agent.